In the practice of diagnostic medicine, it is often necessary or desirable to perform a biopsy, or to sample selected tissue from a living patient for medical evaluation. Cytological and histological studies of the biopsy sample can then be performed as an aid to the diagnosis and treatment of disease. Biopsies can be useful in diagnosing and treating various forms of cancer, as well as other diseases in which a localized area of affected tissue can be identified.
Biopsies are routinely performed on tissue using a biopsy device including a needle set. One known needle set includes an outer cannula having a pointed tip and a tissue receiving opening defined near its distal end, and an inner cannula having an open distal end surrounded by an annular cutting blade. The inner cannula is slidably disposed within the outer cannula so that it can close the tissue receiving opening, thereby cutting tissue prolapsing into the lumen of the outer cannula through the tissue receiving opening. In vacuum-assisted biopsy devices, a vacuum is used to draw the tissue into the tissue receiving opening and to draw excised tissue through the inner cannula to a location proximal of the inner cannula. An irrigation system may also be connected to the outer cannula to provide liquid to facilitate the biopsy. Liquids such as saline may facilitate the biopsy process. The liquid may also provide therapy, such as analgesia provided by an analgesic.
Vacuum-assisted biopsy devices are available in handheld (for use with ultrasound) and stereotactic (for use with X-ray) versions. Stereotactic devices are mounted to a stereotactic unit that locates the lesion and positions the needle for insertion. In preparation for a prone biopsy using a stereotactic device, the patient lies face down on a table, and the breast protrudes from an opening in the table. The breast is then compressed and immobilized by two mammography plates. The mammography plates create images that are communicated in real-time to the stereotactic unit. The stereotactic unit then signals the biopsy device and positions the device for insertion into the lesion by the operator. In contrast, when using the handheld model, the breast is not immobilized. Rather the patient lies on her back and the doctor uses an ultrasound device to locate the lesion. The doctor must then simultaneously operate the handheld biopsy device and the ultrasound device.
During vacuum-assisted biopsies, as the excised tissue advances proximally along the lumen of the inner cannula, a vacuum can be created behind (i.e., distal of) the advancing tissue. At some point in these instances, the excised tissue can stop advancing along the length of the inner cannula because the vacuum behind the excised tissue equals the vacuum in front (i.e., proximal) of the excised tissue that is attempting to draw the excised tissue through the inner cannula.
An exemplary vacuum-assisted biopsy device is described in U.S. Pat. No. 6,638,235, filed on May 23, 2001, and assigned to the same assignee as the instant application, the contents of which are incorporated by reference as though fully set forth herein. In the biopsy device described therein, a leak path between the atmosphere and the outer cannula lumen allows the portion of the portion of the inner cannula lumen distal of the excised tissue to equalize in pressure with the atmosphere. This atmospheric equalization relieves the vacuum behind the excised tissue, and aids in drawing the tissue down the length of the inner cannula.
While the vacuum-assisted biopsy device described in U.S. Pat. No. 6,638,235 is an improvement over previous biopsy devices, having two separate connections to the outer cannula (for irrigation and atmospheric equalization) adds to the size of the biopsy device.